It is estimated that up to 8% of children less than 3 years of age and 2% of adults are affected by food allergies (reviewed in 1). While food-induced allergic reactions are the most common cause of outpatient anaphylaxis, 2 the majority of severe reactions of this kind are caused by peanuts and tree nuts. 3, 4 Most plant food allergens can be found among pathogenesis-related proteins, seed storage albumins and globulins, and a-amylase and protease inhibitors.
A previous study by Teuber et al. 6 documented the cloning and sequencing of a gene encoding Jug r 1, a major allergen in the English walnut, Juglans regia. Jug r 1 is a 2S albumin seed storage protein and possesses important homologies in amino acid sequence with other 2S albumin proteins from Brazil nut, cottonseed, castor bean, and mustard.6 Like many 2S albumins, Jug r 1 is synthesized as a precursor protein and cleaved into a large and small subunit joined by disulfide bridges. It is currently believed that patients with life-threatening allergies to walnuts and other tree nuts will rarely become tolerant of these foods 7 and consequently face a lifetime of avoidance. 8 Avoidance, however, is often difficult due to the ubiquitous nature of these foods and the potential for cross-contamination during their processing. 7 
Many approaches to allergen immunotherapy under investigation today are based on a detailed knowledge of the amino acids found in IgE-reactive B-cell epitopes. 9, 10, 11, 12 These reactive sites can be either linear or conformational. Typically, a linear epitope contains a stretch of contiguous amino acids spanning 5-10 residues in the antigen, while residues distant in the primary sequence but proximate in the folded protein comprise a conformational epitope. 13 In recent years, the genes encoding several proteins with allergenicity, such as Jug r 1, have been cloned and expressed using molecular biology techniques. 6, 14, 15, 16 Despite the rapidly increasing number of recombinant allergens, relatively few IgE-reactive B-cell epitopes have been defined. 17-29